1. Field of the Invention
The present invention generally relates to the field of wireless Internet Protocol (“IP”) networks, methods and protocols in personal communication systems (PCS) and, more particularly, to a method and system for dynamically assigning IP addresses in wireless networks without broadcasting over open air.
2. Description of the Related Art
Emerging IP (Internet Protocol) based wireless networks use IP protocols for transport and control of data and/or voice over open air and over wired IP networks. As a result, mobile stations utilizing the IP networks are required to dynamically obtain IP addresses when the mobile stations move into new IP subnets. Using conventional dynamic IP address allocation mechanisms (e.g., Dynamic Host Configuration Protocol or DHCP), mobile stations and IP address servers (e.g., the DHCP servers) are often required to broadcast IP packets over a wide area.
For example, when a mobile station first enters a new IP subnet, typically it does not possess the address of the IP address servers of the new IP subnet. Therefore, the mobile station usually broadcasts packets to the DHCP server of the new IP subnet to request assignment of new IP addresses. These packets contain IP broadcast addresses as their IP destination addresses and are sent by standard IP network devices to every IP host on the IP subnet, including all the wireless IP hosts. For example, if N cells are supported by the same IP subnet, these DHCP messages would be broadcast to all wireless IP hosts in all the N cells. This wide area broadcast is a waste of scarce wireless resources.
FIG. 1 is a schematic block diagram which illustrates unnecessary broadcasting of DHCP messages to mobile stations in a conventional wired IP Network or subnet. Here, mobile station A is shown as having recently entered a new cell 50 which is served by base station 3 (BS3). All mobile stations served by all the base stations BS1, BS2, BS3 (shown in FIG. 1) belong to the same IP subnet 20.
By moving into a new cell 50, mobile station A may change subnet and hence be required to request a new address. When mobile station A recognizes that it has moved into a new cell, it uses standard DHCP procedures to validate its current IP address and/or request a new IP address, if necessary. An exemplary simplified standard procedure for a mobile station to use DHCP to obtain a new IP address or to verify its current IP address is:                (1) The mobile station broadcasts a DHCPDISCOVER message on a local IP subnet in a broadcasted IP packet (i.e., a packet containing a broadcast destination IP address). Here, the mobile station may include options where values for its IP address are suggested, such as its current IP address; and        
(2) a DHCP server responds with a DHCPOFFER message upon receiving the DHCPDISCOVER message. The DHCPDISCOVER message will contain the IP address assigned to the mobile station. The DHCP servers may also broadcast the DHCPOFFER messages back to the clients.
A mobile station may receive multiple DHCPOFFER messages from multiple servers. Therefore, after receiving such DHCPOFFER messages, the mobile station broadcasts a DHCPREQUEST message back to the servers. The DHCPREQUEST message may also be used to acknowledge acceptance of an address assigned by a particular server to a mobile station, and to decline offers from other servers.
Using the previously described conventional DHCP and standard IP network devices, all the DHCP messages broadcast from a requesting mobile device and the DHCP servers are routed to every mobile station on the same IP subnet serving the requesting mobile station. Broadcasting IP packets in this manner to all mobile stations in a “common” IP subnet wastes scarce, valuable resources in the wireless network and consumes power within the mobile stations, since no other mobile station in the IP subnet needs to receive the transmitted IP packets.
This waste becomes an acute problem when PPP (point-to-point protocol) is used to support IP transport of packets over Code Division Multiple Access (CDMA) networks (e.g., as suggested by the Third Generation Partnership Project II or 3GPP2). Specifically, when PPP is used, base stations are required to send a separate copy of the broadcast packet to each mobile station, which can lead to even more unnecessary signaling traffic over the air.
In computer-related networking or telecommunications, the point-to-point protocol is used for communicating information between a source and a destination over a point-to-point link. PPP is widely used for transmitting Transmission Control Protocol/Internet Protocol (TCP/IP) packets over dial-up telephone connections, such as between a general purpose computer and an Internet Service Provider (ISP). TCP/IP is a set of protocols developed by the United States Department of Defense for communications over interconnected, sometimes dissimilar, networks and has become the de facto standard for data communications over various networks, including the Internet. The point-to-point protocol provides a standard methodology for transporting multi-protocol datagrams of information over point-to-point links. PPP comprises three main components: (1) a methodology for encapsulating multi-protocol datagrams, (2) a link control protocol (LCP) for establishing, configuring and testing the data link connection, and (3) a family of network control protocols (NCPs) for establishing and configuring different network-layer protocols.
An end-user sets up a PPP session between the source, e.g., a general purpose computer or telecommunication device, and a destination (which can also be a general purpose computer or telecommunication device) for transmitting data or information thereto. In a PPP session, once the initial negotiation phases are successfully completed, a session identifier is associated with the connection, thereby identifying the PPP session. Typically, a single PPP connection exists between an end user's computer and the destination, e.g., an Internet service provider (ISP) or another computer connected to the Internet. The PPP session is closed when the end-user of the network system completes the data or information transfer.
A PPP (point-to-point protocol) packet or frame consists of the user data and any headers of other protocols being encapsulated by the PPP. The frame is also provided with a PPP header. The PPP header contains the information necessary to identify and maintain an associated PPP session.
Encapsulation in PPP treats a collection of structured information as a single entity without affecting or taking notice of its internal structure. Thus, a message or packet constructed according to one protocol (such as a TCP/IP packet) may be taken with its formatting data as an undifferentiated stream of bits that is then broken up and packaged according to the higher level point-to-point protocol to be sent over a particular network.
Code Division Multiple Access (CDMA) broadcast channels (e.g., the paging channel) can also be used to transmit IP packets. However, conventional broadcast channels used in CDMA networks are typically not designed for such time-sensitive traffic, and no mechanism or standard is currently available for carrying IP packets over such CDMA broadcast channels. Accordingly, there is a need for a method for supporting dynamic IP address assignment without over the air broadcasting messages of the protocol used for address assignments.